Once exoplanets, worlds orbiting other stars, were the stuff of science fiction but now we know of literally hundreds of real alien planets circling other stars. Astronomers can infer and sometimes measure the statistics and properties of exoplanets and some are extreme! Here are some record-breaking alien worlds.

The planets in our Solar System have been known to mankind for millennia, often referred to by the ancient civilizations as the wandering stars. After the discovery of powerful telescopes we were able to see further into our Solar System and discover many distant objects and dwarf planets. However within the last 16 years astronomers have started to dedicate much more time to the search of other worlds in orbit around other stars beyond the realm of our Solar System. The current number of exoplanets (Extra-Solar planets) discovered as I type these words is 564 and new planets are being discovered regularly. You can keep up to date with the latest count at NASA’s Planetquest site. Each of these new worlds discovered are different and exciting and gives us some insight into the scale of our Universe.

Pulsar planets like PSR B1620-26b are all that remains in dead solar systems. They are constantly beamed with intense radiation. (Image credit: NASA)

1.The oldest exoplanet that has been discovered is ‘PSR B1620-26b’. This exoplanet is almost 13 billion years old, and has been nicknamed the ‘Methuselah’ planet. This planet was first discovered in 1993 but its discovery was only confirmed in 2003. This planet is located inside a globular cluster (M4), which is a sphere of stars held together by gravity. This globular cluster is located in the constellation of Scorpius the Scorpion. The star that this planet orbits is actually a pair of stars, one a pulsar and the other a white dwarf star.

2. The densest exoplanet discovered to date is the planet Janssen (55 Cancri e). This planet also has a year of just less than 18 hours. Originally when it was discovered it was thought to have an orbit of 2.8 days but on further inspection it was realised that this planet moved in very quickly. 55 Cancri e, is a little bigger than Earth but no where near as large as a gas giant planet. Astronomers using Canada’s MOST telescope were able to detect a slight dip in the star’s light on the planet’s passing across it. Although very slight, astronomers have been able to work out the planet’s mass, which is thought to be almost 9 times that of the Earth, meaning that this planet is almost as dense as pure lead, meaning this is the densest planet discovered so far!

Artist’s concept of the star Fomalhaut and Dagon,the Jupiter-type planet that has been observed by the Hubble Space Telescope . A ring of dusty debris appears to surround Fomalhaut as well. The planet Dagon orbits the 200-million-year-old star every 876 years. (Image credit: ESA, NASA, and L. Calcada (ESO for STScI))

3. In contrast to our fast moving planet with such a short year, the exoplanet Fomalhaut b (also known as Dagon) has the longest year. One orbit for this planet around its parent star is approximately 320 000 days or 876 years. This planet was discovered in November 2008, and thought to be around the same size as Jupiter; however it may have a mass of three times that of Jupiter’s. This planet is in orbit around the star Fomalhaut which is located 25 light years away from Earth.

4. Some exoplanets are located around distant stars in the depths of our galaxy perhaps located hundreds of light years away from us. However the closest star with a known exoplanet is the star Epsilon Eridani which is a mere 10.4 light years away from planet Earth. Discovered in 2000, the planet AEgir (Epsilon Eridani b) has an orbit of just less than 7 years and a mass of less than one Jupiter mass.

With an estimated temperature of just 50K, OGLE-2005-BLG-390L b is the also chilliest exoplanet yet discovered. (Image credit: ESO)

5. The exoplanet which is located furthest away from planet Earth is located in orbit around the star OGLE-2005-BLG-390L. This star is located a staggering 21 000 light years away in the constellation of Scorpius the Scorpion. This planet was first discovered at the La Silla observatory in Chile with further observations conducted at the Perth Observatory in Australia. The first part of its name comes from Optical Gravitational Lensing Experiment (OGLE), one international group busy with the search for distant worlds.

As Gliese 581e is 20.5 light years away, its inhabitants (if such there are) will shortly hear how the 1991 Gulf War ended. (Image credit: ESO)

6. Exoplanets come in all sizes and the lightest exoplanet discovered to date is a planet in the Gliese 581 system. Gliese 581 is a small red dwarf star 20.5 LY distant it in the constellation of Libra the scales. This star has 4 known planets orbiting around it. Gliese 581 e is the planet orbiting closest to its parent star, and has a year of only 3.15 days. This planet is the least massive as it has a mass only 2 times that of the Earth and is most likely a small rocky planet. This is also the most recent planet to be discovered in the Gliese system discovered in April 2009.

7. The most massive exoplanet was only discovered in February 2011. This is the planet CD-35 2722b in orbit around its parent star CD-35 2722. This star is located almost 70 light years away from Earth, and is a gas giant planet with a mass 31 times that of Jupiter’s. As time goes on hopefully we will learn much more about this large planet.

HIP13044b, a very alien world indeed. (Image credit: ESO)

8. All of the exoplanets discovered to date have been discovered within our Milky Way galaxy. However in November 2010, astronomers discovered a planet orbiting another star that is from another galaxy. The star HIP 13044 and planet HIP 13044b are located 2000 light years distant and are within the Milky Way. However this star is believed to have been part of another galaxy that was swallowed by the Milky Way around 6 billion years ago. The star planet has an orbit of just over 16 days and has a mass of 1.25 Jupiters.

In 16 years 564 new worlds have been discovered. A lot is still to be learnt about each of these strange and fascinating worlds, so as we explore further into the depths of our galaxy and perhaps discover yet more new planets, we learn a little more about the record breaking exoplanets as well as giving an insight on what exists out beyond our Solar System.

Very interesting article Martina. When I was at school in the 1970s it was believed that Barnards Star, the second closest star system to us, had two planets going around it, this being inferred from a wobble in its proper motion. However this turned out to be a false alarm and it turned out that what was being observed was movement of the Earth caused by Jupiter and Saturn. It just goes to show how tiny the measurements involved are!

Welcome to Astronotes

Hello, I’m Heather, welcoming you to Astronotes, the Armagh Observatory and Planetarium’s official blog. Here you will find the latest news and views from all those who work in our organisation, from the fascinating worlds of astronomy and space exploration. We hope you will come here to learn what is hot and exciting, profound or even weird from worlds beyond ours .
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Armagh Observatory opened in 1790

Armagh Planetarium opened in 1968

Professor Louise Harra

Director of Armagh Observatory and Planetarium Michael Burton, on top of Mopra Rock in the Warrumbungles National Park of New South Wales. The 22m diameter Mopra radio telescope, star of the tale told here, lies below and behind him. (image credit: Michael Burton)